Obesity has become a worldwide epidemic. In the United States, more than 60% of the population is overweight or obese. Weight conditions are typically classified based on body mass index (BMI), which is calculated by the following formula:
BMI = weight (kilograms)
Overweight is defined as a BMI between 25 and 29.9 kg/m2, and obesity is defined as a BMI of 30 kg/m2 or greater.
Although genetic factors influence body weight, diet and lifestyle have major effect as well. The number of overweight and obese people in the United States increased by one third between 1990 and 2000, due in part to larger portion sizes, increased availability of high-calorie foods such as cheese and soft drinks, and decreased physical activity.
Obesity is a strong risk factor for several chronic diseases, including hyperlipidemia, cardiovascular disease, cerebrovascular disease, hypertension, type II diabetes, cholelithiasis, several types of cancer (particularly those arising in the breast, prostate, and colon), dementia, sleep apnea, pseudotumor cerebri, osteoarthritis of the hips and knees, and infertility.
In addition to the contributions of increased energy intake and decreased physical activity to the risk of obesity, genetic factors play an important role. Dozens of genes coding for hormones, neurotransmitters, and receptors have been associated with weight control. Several mechanisms are being investigated as a basis for possible pharmacologic therapies. These include leptin, ghrelin, and melanocortin. Depression, anxiety, and eating disorders may also contribute to habits that promote unhealthy weight gain.
DiagnosisA diagnosis of obesity requires a complete history and physical examination, with special attention to medications, herbal remedies, nutritional and exercise history, risk factors for coronary artery disease, and family history of thyroid and cardiac diseases.
BMI calculation is commonly used to estimate the severity of overweight.
Anthropometric measures also include waist circumference, waist-to-hip circumference ratio, and body-fat determination, which is based on skin-fold thickness or bioimpedance.
Laboratory testing includes fasting glucose and insulin concentration, thyroid-stimulating hormone and free T4 hormone levels, renal function, lipid panel, complete blood count (CBC), and aspartate aminotransferase (AST) to screen for hepatic steatosis.
The therapeutic essentials for treating obesity are diet, exercise, and lifestyle modification that reduce energy intake and increase energy expenditure. Nutritional interventions are discussed below. Physical activity helps to retain lean body mass and may better prepare patients to keep weight off after the initial loss,1 in comparison with food restriction alone.
Several medical therapies are available. However, long-term results of pharmacotherapy are only moderate, and weight is regained once the patient discontinues the medications.2 Recent evidence suggests that a combination of pharmacotherapy and behavior therapy achieves better results than either modality used alone.3
Medications that are commonly used (but not necessarily recommended) include:
Appetite suppressants. Examples are sibutramine, phentermine, benzphetamine, phendimetrazine, and diethylpropion.
Orlistat. This gastric lipase inhibitor decreases the absorption of dietary fat. However, when using this medicine it is necessary to supplement diet with fat-soluble vitamins and phytonutrients.
Bariatric surgery has been used successfully in morbidly obese patients (BMI >40). Gastric bypass and banding are the most frequently used surgeries. Complications such as nutrient malabsorption and infection are common and lead to the 1% to 2% mortality risk associated with these procedures.
Certain personality and behavioral factors are characteristic of those who succeed at maintaining weight loss. These factors include developing coping skills that prevent using food for comfort; increasing self-efficacy with respect to weight control4; engaging in high levels of physical activity (approximately 1 hour per day); choosing a low-calorie, low-fat diet; eating breakfast regularly; self-monitoring weight; and maintaining a consistent eating pattern through the 7-day week.5 The characteristic behaviors of those who keep weight off are documented and updated through the National Weight Control Registry, available at: http://www.nwcr.ws/.5
Patients should be advised to avoid dietary supplements promoting weight loss. Reviews of their effectiveness indicate a lack of efficacy for chitosan, chromium picolinate, Garcinia cambogia, glucomannan, guar gum, hydroxy-methylbutyrate, plantago psyllium, pyruvate, yerba mate, and yohimbe.6 Ephedra-containing formulas have been found effective for weight control, particularly when combined with aspirin. However, the risk-to-benefit ratio of this combination is prohibitively high due to potential adverse cardiovascular effects of ephedra, as well as potential gastrointestinal damage caused by aspirin.
Although genetic factors contribute to obesity, the increased prevalence of this condition during the last century confirms that obesity is the result of gene/environment interactions.7 The Western diet, which provides highly palatable, energy-dense foods rich in fat and sugar, is conducive to weight gain. These foods activate reward systems in the brain, up-regulate the expression of hunger signals, and blunt the response to satiety signals, promoting overconsumption.8
Common short-term restrictive diets that limit portion sizes tend not to produce long-term weight loss. A better approach is a permanent change in the type of foods individuals select and in physical activity. Individuals who consume foods lower in energy density and higher in water and fiber (eg, salads, soups, vegetables, and fruits) instead of foods high in energy density experience early satiety and spontaneously decrease food intake. This strategy has produced weight loss in several clinical studies.9 Because it allows for the intake of larger portions that provide satiety,10,11 it fosters continued adherence.
The following steps reduce the energy density of the diet and promote weight control:
Reducing dietary fat. Aside from holding over twice as many calories per gram as protein and carbohydrate (9 calories per gram of fat, compared with 4 for protein or carbohydrate), dietary fat promotes passive overconsumption of energy, and the addition of fats to meals results in fat storage rather than fat oxidation. These mechanisms may explain why the prevalence of overweight worldwide is directly related to the percentage of fat in the diet, and why low-fat diets have been consistently shown to promote moderate weight loss.12 Common sources of fat are meats, dairy products, fried foods, and added oils.
Choosing foods high in complex carbohydrates and fiber. Populations in Asia, Africa, and elsewhere with diets high in complex carbohydrates tend to have a low incidence of obesity. The whole grains and legumes in these diets also provide fiber. Fiber is filling, but contributes little to overall calorie intake. Studies show that fiber intake is inversely associated with body weight and body fat.13
Following low-fat, vegetarian diets. Several studies have found that vegetarians tend to be slimmer than omnivores, which is not surprising given that grains, legumes, vegetables, and fruits are low in fat and high in complex carbohydrates and fiber.14 Randomized trials show that low-fat vegan diets promote greater weight loss than typical low-fat diets, and they also improve plasma lipids, insulin sensitivity, and other measures.10 A study of a vegetarian diet in heart patients, used in combination with exercise and stress management, showed sustained weight loss over a 5-year period.15
Minimizing sugars. Sucrose, high-fructose corn syrup, and other sugars add calories without producing satiety. Increased intake of sweetened beverages is associated with a rise in obesity.16
Low-carbohydrate diets have been popular, but they have not been found superior to either low-fat, high-carbohydrate, or calorie-controlled diets over a 12-month period.17 Such diets icrease plasma low-density lipoprotein concentrations, sometimes severely, in approximately one third of users. They also cause a sustained increase in urinary calcium losses.18
Vegetarian diet, nondairy, low-fat
What to Tell the Family
Obesity contributes to many chronic illnesses, but it may be prevented and successfully treated in most individuals through a diet low in fat and sugar, and high in fiber, along with regular physical activity. Well-planned, low-fat vegan and vegetarian diets are particularly healthful and effective.
3. Wadden TA, Berkowitz RI, Womble LG, et al. Randomized trial of lifestyle modification and pharmacotherapy for obesity. N Engl J Med. 2005;353:2111-2120.
4. Byrne SM. Psychological aspects of weight maintenance and relapse in obesity. J Psychosom Res. 2002;53:1029-1036.
8. Erlanson-Albertsson C. How palatable food disrupts appetite regulation. Basic Clin Pharmacol Toxicol. 2005;97:61-73.
10. Barnard ND, Scialli AR, Turner-McGrievy G, Lanou AJ, Glass J. The effects of a low-fat, plant-based dietary intervention on body weight, metabolism, and insulin sensitivity. Am J Med. 2005;118:991-997.
12. Jequier E, Bray GA. Low-fat diets are preferred. Am J Med. 2002;113(suppl 9B):41S-46S.
13. Berkow S, Barnard ND. Vegetarian diets and weight status. Nutr Rev 2006;64:175-188.
14. Slavin JL. Dietary fiber and body weight. Nutrition. 2005;21:411-418.
18. Yancy WS, Olsen MK, Guyton JR, Bakst RP, Westman EC. A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia. Ann Int Med.2004;140:769-777.